ElMd 


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MEMOIR 


Wgeld  hall 


ON 


A NEW  KIND  OF 


MOVABLE  DAM. 


S.  JANICKI,  Engineer, 

DIRECTOR  OF  THE  MOSKVA  NAVIGATION  COMPANY. 


f 


TRANSLATED  BY 


LIEUT.  COL.  WILLIAM  E.  MERRILL, 

CORPS  OF  ENGINEERS,  U.  S.  A. 


WASHINGTON: 


LIBRARY  OF  THE 
UNIVERSITY 
OF  ILLINOIS 


COLLEGE  OF 
ENGINEERING 


From  tLc  libranj  of 

JOHN  AUGUSTUS 
OCKERSON 

CL  AS  5 O r J & 7 3 
Presented.  AAaiJ  1,1024 
bii  hisTWidow  CLA.RA 
SHACKELFORD  OCKERSON 


627.3 

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tno.5 


MEMOIR 


ON 

A NEW  KIND  OF 


MOVABLE 


BY 


DAM. 


S.  JANICKI,  Engineer, 

DIRECTOR  OF  THE  MOSKVA  NAVIGATION  COMPANY. 


TRANSLATED  BY 

LIEUT.  COL.  WILLIAM  E.  MERRILL, 

CORPS  OF  ENGINEERS,  U.  S.  A. 


WASHINGTON: 

1883. 


Digitized  by  the  Internet  Archive 
in  2017  with  funding  from 

University  of  Illinois  Urbana-Champaign  Alternates 


https://archive.org/details/memoironnewkindoOOjani 


United  States  Engineer  Office, 

Cincinnati , 0.,  September  24.,  1883. 

General : 

In  order  to  keep  up  with  the  latest  improvements  in  movable  dams, 
I have  the  honor  herewith  to  forward  a translation  of  a recent  pamphlet 
by  the  Russian  Engineer  Janicki,  which  I think  merits  reproduction, 
although  no  dams  have  yet  been  built  on  the  system  which  he  has 
invented. 

Respectfully,  your  obedient  servant, 

Wm.  E.  Merrill, 

Lt.  Col.  Engineers. 

Brig.  Gen.  H.  G.  Wright, 

Chief  of  Engineers , U.  S.  A. 


A NEW  SYSTEM  OF  MOVABLE  DAMS  WITH  HORSES. 


By  S.  Janicki, 

Director  of  the  Moskva  Navigation  Company. 


In  order  to  point  out  the  advantages  of  the  new  kind  of  movable  dam 
which  I have  invented,  I will  first  briefly  recall  the  principal  systems 
thus  far  used  for  such  dams. 

This  review,  while  pointing  out  the  successive  modifications  of  exist- 
ing types,  will  at  the  same  time  serve  to  prove  that  the  new  system 
under  discussion  contains  nothing  which  is  wholly  new,  and  that  it  is 
in  fact  only  a combination  of  parts  belonging  to  types  already  known 
and  approved  by  experience. 

We  believe  that  by  this  discussion  we  shall  allay  a certain  legitimate 
timidity  felt  by  practical  engineers  at  applying  on  a large  scale  a system 
which  in  its  novel  combinations  has  nowhere  yet  been  tested. 


4 


The  first  movable  apparatus,  employed  to  increase  the  height  of  water 
aboye  fixed  dams,  consisted  of  wickets,  or  shutters,  with  horizontal  axes 
of  rotation  normal  to  the  thread  of  the  stream,  placed  at  the  lower  ends 
of  these  shutters. 

To  allow  floods  to  pass,  these  shutters  were  dropped  horizontally 
down-stream  ; when  lifted,  to  raise  the  water-level,  they  were  supported 
behind  by  props  abutting  against  the  down-stream  slope  of  the  dam. 

This  primitive  type  is  very  ancient ; we  find  the  earliest  description 
of  it  in  the  work  of  DeLalande,  published  in  1778,  ( Traite  des  Travaux 
de  Navigatioji),  in  which  reference  is  made  to  such  a movable  dam  on 
the  river  Orb. 

Various  modifications  of  this  primitive  type  were  afterwards  made. 
In  France,  between  1832  and  1836,  M.  Thenard  built  a dam  with  similar 
movable  shutters  on  the  weir  of  the  river  Isle,  with  this  difference,  that 
in  front  of  the  principal  shutters,  which  fall,  as  we  have  just  stated, 
down-stream,  he  placed,  at  the  suggestion  of  M.  Mesnager,  a first  rank 
of  similar  shutters  which  fell  up-stream.  These  are  called  counter- 
shutters. 

This  first  rank  of  auxiliary  up-stream  shutters  supported  the  water 
pressure,  when  upright,  by  means  of  tie  rods  or  chains  fastened  to  the 
upper  slope  of  the  dam ; the  object  of  this  rank  was  to  facilitate  the 
setting  up  of  the  main  shutters.  In  fact,  when  the  movable  dam  had  to 
be  raised  against  a strong  current,  the  auxiliary  shutters  (the  counter- 
shutters) were  released  from  their  horizontal  position  and  were  righted 
by  the  mere  force  of  the  current.  Under  the  shelter  of  this  first  rank, 
the  principal  shutters  could  be  raised.  This  was  done  by  the  men  in 
charge  of  the  dam,  who  walked  on  the  lower  slope  and  put  into  place 
the  feet  of  the  props.  As  soon  as  the  pressure  of  water  created  by  the 
first  rank  was  transferred  to  the  principal  rank  of  shutters,  well  braced 
by  their  props,  the  first  (auxiliary)  rank  was  laid  down,  so  that  it  might 
be  used  again  at  the  next  raising  of  the  dam. 

To  open  dams  of  this  kind  while  under  pressure,  the  feet  of  the  props 
were  pushed  by  a side  thrust  away  from  the  shoulders  or  sockets 
against  which  they  rested.  To  assist  in  this  somewhat  awkward  opera- 
tion, and  to  save  the  men  in  charge  from  the  necessity  of  getting  upon 
the  lower  slope  of  the  dam,  M.  Thenard  introduced  on  the  Orb  dam 
another  improvement,  a notched  bar,  which  engaged  the  feet  of  the 
props  and  enabled  them  to  be  dropped  in  succession.  This  notched 
bar  is  the  tripper , which  is  still  used  for  lowering  the  shutters  or  wickets 
of  dams  of  the  type,  of  which  I shall  speak  further  on,  bearing  the  name 
of  M.  Chanoine. 


The  system  which  we  have  just  described,  and  which  is  named  after 
M.  Th6nard,  was  gradually  improved  by  him,  and  was  applied  to  the 
highest  lifts.  M.  Thenard  endeavored  to  place  on  the  tops  of  the 
counter-shutters  a narrow  foot-walk,  upon  which  the  men  whose  duty 
it  was  to  raise  the  lower  shutters  could  stand.  Finally,  in  order  to  get 
rid  of  the  counter-shutters,  he  proposed  to  place  above  the  rank  of  prin- 
cipal shutters  a needle-dam  on  the  Poir6e  system,  whose  closure  by 
needles  would  permit  the  easy  raising  of  the  rank  of  shutters.  This 
needle-dam  was  also  to  act  as  a service-bridge,  upon  which  the  men 
could  walk  who  were  to  raise  the  lower  shutters.  In  this  way  the 
manoeuvring  of  the  dam  could  be  accomplished  with  ease  and  safety. 
But  experience  has  proved  that  with  the  increase  in  the  heights  of  shut- 
ters, and  in  the  size  of  the  rivers  on  which  it  was  desired  to  use  this 
system,  its  practical  application  became  more  and  more  difficult  The 
raising  of  the  counter-shutters  by  the  current  cannot  but  cause  very 
heavy  shocks,  which  are  dangerous  to  the  anchorage  of  these  counter- 
shutters ; similarly,  the  raising  of  the  principal  shutters  was  difficult  and 
dangerous.  Since  in  France  they  were  seeking  to  apply  movable  appa- 
ratus, not  only  for  the  purpose  of  increasing  the  heights  of  weirs,  but 
also  for  closing  navigable  channels,  which  required  shutters  of  great 
height,  the  system  of  MM.  Thenard  and  Mesnager  fell  into  disuse; 
that  of  M.  Chanoine  took  its  place.  We  should  add,  however,  that  the 
Th6nard-Mesnager  system,  with  various  modifications  of  detail,  is  still 
used  with  considerable  success  by  English  engineers  in  the  movable 
parts  of  the  great  dams  on  the  rivers  of  India.  (See  Movable  Dams  in 
Indian  Weirs  by  Robert  Buckley , Minutes  of  Proceedings  of  the  Institution 
of  Civil  Engineers , Vol.  IX.,  Session  1879-80,  part  //.).  They  have 
used  on  these  Indian  dams  the  shutters  and  counter-shutters  of  MM. 
Thenard  and  Mesnager  up  to  pressures  of  more  than  10  feet.  In  the 
Indian  dams  it  is  easy  to  close  shutters  and  counter-shutters  of  this 
system  when  there  is  from  8 to  10  feet  of  water  on  the  sills  of  the  dams. 
They  are  opened  rapidly  and  easily,  but  the  arrangements  are  such  as 
to  require  the  insertion  in  the  dam  of  masonry  piers  with  open  spaces 
between  them  not  greater  than  from  20  to  50  feet. 

The  existence  of  permanent  piers  so  close  together,  besides  increasing 
the  cost  of  building  such  dams,  is  a hindrance  to  free  navigation.  For 
this  general  reason,  and  more  especially  when  we  have  to  deal  with 
rivers  which  freeze  and  are  subject  to  ice-floods,  the  methods,  which 
have  been  elaborated  on  the  English  East  Indian  rivers,  cannot  be 
applied  in  other  countries.  As  we  have  seen  above,  it  is  especially  the 
difficulty  of  raising  the  shutters  against  the  current  which  has  been  the 


6 


chief  cause  for  the  abandonment  in  France  of  the  Thenard-Mesnager 
system. 

M.  Chanoine,  in  order  to  avoid  this  difficulty,  concluded  to  change 
the  position  of  the  axis  of  rotation  of  the  shutters.  This  axis  was  placed 
by  M.  Chanoine,  not  immediately  on  the  floor  at  the  foot  of  the  shutter, 
but  at  its  centre  (or  a little  below  it),  on  the  head  of  a horse  which,  in 
its  turn,  could  rotate  around  a base  fastened  to  the  floor.  This  well 
known  arrangement  (I  do  not  intend  to  describe  it  in  detail  here)  per- 
mitted the  shutter  to  be  raised  by  pulling  on  its  base.  The  shutter  thus 
remained  on  the  swing  while  coming  up,  and  did  not  give  the  current 
too  much  hold. 

By  placing  the  axis  of  rotation  of  the  wickets  at  about  one-third  their 
height,  they  could  be  rendered  automatic ; that  is,  they  would  swing  of 
themselves  when  the  upper  level  exceeded  the  prescribed  height. 

The  wickets  of  M.  Chanoine’s  system  are  lowered  by  means  of  the 
tripper,  invented,  as  we  have  seen  above,  by  M.  Thenard. 

In  spite  of  the  advantages  of  the  new  arrangement,  and  of  the  im- 
provements in  details  successively  introduced  into  the  Chanoine  system 
to  facilitate  raising,  and  lately  for  lowering  also,  the  authorities  have 
everywhere  begun  to  place  above  dams  of  this  system  a special  service- 
bridge  of  trestles  of  the  style  invented  by  M.  Poir6e.  In  the  latest  ap- 
plication of  the  swinging  wickets  of  M.  Chanoine  (at  the  La  Mulati^re 
dam  at  Lyons)  Engineer  Pasqueau,  struck  by  the  necessity  of  devising 
a new  kind  of  movable  dam  which  could  be  used  for  dams  with  high 
lifts  and  wide  passes  without  intermediate  piers , devised  and  applied  an 
entirely  novel  arrangement  by  which  he  could  dispense  with  the  tripper. 
Trippers,  as  is  well  known,  are  complicated  pieces  of  mechanism,  which 
practically  limit  the  free  opening  between  the  piers  of  a dam  to  a max- 
imum of  about  50  meters  [164  feet]. 

This  new  arrangement  of  M.  Pasqueau,  which  is  very  ingenious  in 
its  simplicity,  consists  in  resting  the  props,  which  hold  up  the  horses 
of  the  wickets,  against  a hurter  and  slide  of  a peculiar  shape  which  is 
fastened  to  the  floor.  This  slide  has  two  steps — the  first  supports  the 
foot  of  the  prop  when  the  horse  is  upright ; the  other  step  is  oblique 
and  serves  to  push  the  prop  sideways  towards  a horizontal  groove  in 
which  its  foot  can  slide  freely  to  the  rear;  that  is,  the  prop  can  lie  down. 
(See  Barrage  de  la  Mulattire,  Notice  sur  le  nouveau  systbne  dcs  hausses 
par  M.  A.  Pasqueau , Ingbiicur  des  Ponts  et  Chaus  sees.  Lyon , imprimerie 
Pitrat  aim,  1879) 

The  double-stepped  hurter  of  M.  Pasqueau,  against  which  rests  the 
prop  of  the  wicket,  permits  the  wicket  to  be  raised,  to  be  swung,  and 


to  be  laid  down,  according  to  the  necessities  of  the  case,  by  a pull  which 
is  always  in  one  direction,  and  parallel  to  the  thread  of  the  stream. 

At  the  La  Mulatiere  dam  a service-bridge  of  trestles,  placed  above 
the  rank  of  wickets,  is  used  in  the  manoeuvres  just  named. 

Without  going  into  a description  of  the  other  kinds  of  movable  dams, 
whose  movable  parts  are  likewise  provided  with  horizonral  axes  of  rota- 
tion normal  to  the  thread  of  the  current,  I pass  to  the  system  which  is 
probably  the  most  generally  adopted  at  this  present,  that  of  M.  Poiree. 

This  system,  as  is  known,  consists  of  a series  of  trestles  whose  planes 
are  parallel  to  the  thread  of  the  current.  Naturally  the  axis  of  rotation, 
placed  at  the  bottom  of  these  trestles,  is  likewise  parallel  to  the  thread 
of  the  current.  This  axis  enables  the  trestles  to  turn  around  journal 
boxes  fastened  to  the  floor.  When  the  series  of  trestles  is  upright,  and 
connected  at  the  top  to  each  other  and  to  the  abutments,  it  forms  a 
metallic  skeleton,  which  serves  as  a support  to  the  true  screen  or  curtain 
of  the  dam.  This  movable  screen  is  either  composed  of  the  classic 
needles  of  M.  Poiree,  or  of  the  horizontal  gates  of  the  system  of  M. 
Boul6.  The  very  simple  apparatus  for  closing,  which  I have  just 
named,  has  the  immense  advantage  of  transforming  the  whole  length 
of  the  dam  into  an  overfall,  and  it  thus  permits  the  adaptation  of  Poir6e 
trestles  to  dams  with  high  falls,  which  could  not  be  done  if  needles 
were  used. 

We  see  from  what  precedes  that  the  great  difference  between  movable 
dams  on  the  Th6nard-Mesnager  and  Chanoine  systems,  and  those 
which  use  Poiree  trestles,  is  that,  in  the  first-named  dams,  the  screens, 
which  close  the  dams  with  more  or  less  tightness,  are  fastened  to  the 
skeletons  themselves,  while  in  the  Poiree  trestle-dams  the  skeletons  are 
only  used  as  supports  for  independent  screens,  which  are  raised  and 
carried  to  shore  when  the  dam  is  to  be  opened  and  laid  down. 

Being  under  the  necessity  of  planning  a dam  for  a very  wide  river 
(400  meters)  [1312  feet],  whose  floods  are  very  rare  and  slow,  thus 
always  giving  time  to  raise  and  carry  to  shore  the  parts  of  the  movable 
screen,  I thought  of  applying  on  this  river  the  system  of  Poiree  trestles 
with  horizontal  Boule  gates,  modified  in  conformity  with  the  type  used 
on  the  river  Moskva. 

But  the  use  of  trestle  dams  on  very  wide  rivers,  where  one  is  obliged 
to  avoid  intermediate  piers,  has  many  inconveniences.  In  the  first 
place,  as  is  known,  all  of  the  trestles  have  to  be  dropped  in  the  same 
direction.  Hence,  since  this  operation  can  only  be  begun  at  one  end, 
it  follows  that  the  time  required  to  throw  down,  or  to  raise  a long  dam, 
would  be  too  great.  In  the  second  place,  and  this  is  extremely  im- 


8 


portant,  all  of  the  trestles  are  kept  in  a vertical  position  by  the  movable 
top-fastenings,  which  connect  them  with  each  other  and  with  the  abut- 
ments, and  the  accidental  rupture  of  these  fastenings  at  a single  point, 
during  the  raising  or  lowering  of  the  dam,  may  cause  the  simultaneous 
fall  of  all  the  trestles.  In  the  third  place,  the  sanding  up  in  a wide 
river  of  a considerable  length  of  dam,  while  the  trestles  are  down,  may 
make  it  very  difficult  to  erect  the  dam.  Fourthly  and  lastly,  when 
trestles  are  used  on  dams  whose  lifts  are  above  the  average,  they  have 
to  be  quite  high,  and  their  thickness  is  necessarily  considerable,  and  as 
they  lie  down  with  several  in  a pile,  they  call  for  deeper  recesses  in  the 
floor  to  contain  them.  This  necessitates  an  increased  thickness  of  floor, 
thus  augmenting  the  cost  of  construction,  at  the  same  time  that  the 
deeper  recess  increases  the  chances  of  sanding  up. 

All  of  these  considerations  make  us  think  that  in  practice  Poiree 
trestle  dams  should  no  longer  be  used  for  pressures  exceeding  3 meters 
[10  feet],  and  that  the  lengths  of  such  dams  should  not  exceed  from  100 
to  150  meters  [328  to  492  feet],  unless  intermediate  piers  are  used. 

The  beautiful  solution  devised  by  Engineer  Pasqueau  for  the  La 
Mulatiere  dam,  which  is  composed  of  Chanoine  wickets  with  double- 
stepped  hurters  for  the  props,  and  a service-bridge  above  for  handling 
the  wickets,  has  its  justification  in  the  local  conditions,  due  to  the  rapid- 
ity of  the  floods  of  the  Rhone. 

I have  concluded  that,  for  rivers  whose  regimens  are  less  torrential, 
such  a solution,  which  requires  a double  construction — a dam  of  wickets 
and  a special  service-bridge  of  trestles — may  be  replaced  by  a solution 
somewhat  simpler. 

In  the  new  solution,  which  I offer,  I make  a complete  separation,  as 
is  done  in  dams  on  the  Poiree  system,  between  the  movable  screen  (the 
curtain)  and  the  skeleton  of  the  dam. 

This  skeleton  is  composed  of  a series  of  horses,  which  can  fold  up 
and  lie  down  horizontally,  parallel  to  the  thread  of  the  stream ; or  stand 
upright,  supported  by  their  props. 

The  up-stream  standards  of  a horse  are  composed  of  two  double 
T-irons,  suitably  connected  and  braced  so  as  to  form  a rigid  frame,  upon 
the  up-stream  side  of  which  the  movable  gates  are  slid  into  place  from 
above,  when  the  dam  is  to  be  closed  up  after  raising. 

Each  frame  has  an  axis  of  rotation  at  its  lower  end,  which  passes 
through  journal  boxes  fastened  to  the  floor. 

A second  axis,  near  mid-height  of  the  frame,  serves  as  a hinge  for 
the  heads  of  the  props,  which  hold  up  the  frames  after  they  are  raised. 
The  feet  of  these  props  rest  against  double-stepped  hurters  of  the  Pas- 
queau system. 


9 


The  width  of  the  frame  forming  the  up-stream  face  of  each  horse  de- 
pends on  the  width  to  be  given  to  the  gates.  As  a rule  this  width  will 
be  the  same  as  the  distance  between  the  trestles  of  the  ordinary  trestle- 
dam.  The  distance  between  the  adjacent  standards  of  two  consecutive 
horses  should  be  the  same  as  the  distance  between  the  standards  of  the 
same  horse,  in  order  that  the  closing  gates  may  rest  indiscriminately, 
either  against  the  standards  of  the  same  horse,  or  against  the  standards 
of  two  consecutive  horses. 

From  what  precedes  it  will  be  seen  that  each  chief  standard  with  its 
prop  forms  a kind  of  trestle,  that  can  fold  up  and  lie  down  horizontally 
parallel  to  the  thread  of  the  stream.  In  order  to  compel  these  folding 
trestles  to  always  keep  in  the  same  vertical  plane,  parallel  to  the  cur- 
rent, while  they  are  being  raised  or  lowered,  we  connect  them  two  by 
two,  as  has  already  been  said,  both  by  means  of  the  axes,  which  serve 
as  hinges,  and  by  the  braces  that  hold  together  the  two  principal  up- 
stream standards. 

It  is  also  practicable  to  add  to  the  rigidity  of  the  system  by  partly 
bracing  together  the  two  props  of  the  same  horse. 

Below  the  front  rank  of  principal  frames  there  is  placed  a second  rank 
of  very  light  frames  similar  to  the  first,  and  connected  with  the  latter  on 
top  by  cross-pieces  parallel  to  the  thread  of  the  stream.  These  two 
frames,  thus  connected  by  cross-pieces,  having  axes  of  rotation  at  the 
points  of  intersection,  form,  in  the  vertical  plane  parallel  to  the  current, 
two  movable  parallelograms  which  can  fall  down  stream  and  lie  hori- 
zontally on  the  floor. 

When  the  system  which  has  just  been  described  is  upright,  supported 
by  the  props,  each  horse  forms  a skeleton,  which  can  serve  both  as  a 
service-bridge  for  placing  and  manoeuvring  the  gates,  and  also  as  a sup- 
port against  the  pressure  of  these  gates. 

The  operation  of  raising  a dam  composed  of  such  horses  is  performed 
as  follows : 

On  a small  railroad  on  the  abutment  there  is  a rolling  crane,  suitably 
weighted,  having  an  adjustable  boom.  This  crane,  which  is  worked  by 
hand,  begins  by  raising  the  first  horse,  which  is  lying  on  the  floor  at  a 
distance  from  the  bank  equal  to  its  width ; as  soon  as  the  feet  of  the 
props  are  heard  to  fall  into  their  seats,  the  crane  ceases  to  raise,  two 
balks  are  placed  from  the  abutment  to  the  cross-pieces  of  this  first 
horse,  on  these  is  laid  the  flooring  of  the  service-bridge,  and  then  the 
crane  is  run  forward  on  this  first  piece  of  dam.  From  this  point  the 
second  horse  is  raised  and  the  second  piece  of  dam  is  erected,  and  so 
on  to  the  end. 


10 


When  once  all  of  the  horses  have  been  raised,  the  horizontal  gates 
are  brought  up  on  trucks  and  are  put  in  place  by  hand,  as  is  done  on  a 
trestle-dam. 

To  perform  the  reverse  operation,  that  is,  to  lower  the  dam,  we  begin 
by  lifting  and  removing  all  the  gates  by  hand  with  the  aid  of  boat- 
hooks, and  with  the  same  crane  we  raise  slightly  the  horse,  which  we 
wish  to  lower,  until  the  prop  falls  off  of  the  sliding  step;  then  the  crane 
lowers  the  horse  and  its  accessories  to  the  floor.  During  this  opera- 
tion the  crane  travels  backward,  until  it  reaches  the  abutment  whence  it 
began  the  operation  of  raising. 

From  this  concise  description,  which  shows  the  idea  which  guided 
us  in  proposing  the  kind  of  dam  of  which  we  are  speaking,  the  advan- 
tages of  using  it  can  be  deduced.  They  are  as  follows : 

1 . By  this  system  a dam  of  any  length  whatever  can  be  built  with- 
out intermediate  piers. 

2.  A dam  of  this  kind  gives  a surface  overflow  along  its  whole  length, 
and  it  is  exactly  as  water-tight  as  a trestle-dam  with  Boule  gates. 

3.  The  operations  of  raising  and  lowering  a dam  of  this  kind  can  be 
begun  simultaneously  from  the  two  abutments  by  means  of  two  differ- 
ent cranes,  and  it  is  even  possible,  if  greater  speed  is  desired,  to  raise 
the  horses  by  means  of  boats  equipped  with  light  shears. 

4.  Should  the  dam  be  sanded  up  at  one  or  at  several  places,  the  rais- 
ing of  the  horses  is  not  hindered,  since  it  is  practicable  to  raise  at  will 
any  of  the  parts  of  the  dam  which  are  not  covered,  and  by  increasing 
the  current  over  the  sanded  parts,  they  are  rapidly  cleaned  off 

5.  Since  in  our  style  of  dam  the  skeleton  serves  also  as  a service- 
bridge,  this  style  must  necessarily  be  cheaper  than  those  in  which  it  is 
necessary  to  place  above  the  true  dam  a special  service-bridge.  For 
the  same  reason  the  operations  of  raising  and  lowering  such  dams  are 
more  rapid. 

6.  The  kind  of  dam  just  described  can  be  used  for  the  greatest  lifts 
without  inconvenience. 

Whilst  we  were  engaged  in  elaborating  the  details  of  the  type  de- 
scribed above,  one  of  our  colleagues,  M.  Gouschkofsky,  Engineer  in  the 
Russian  Corps  of  Ponts  et  Chanss&es , conceived  the  idea  of  the  follow- 
ing additional  modification.  In  the  combination  described,  the  rear 
frame,  which  has  no  other  use  than  to  support  the  cross-pieces  of  the 
foot-bridge,  instead  of  having  its  points  of  rotation  low  down  on  the 
floor,  might  have  had  them  on  the  props  themselves. 

In  order  that  a horse,  thus  modified,  may  be  able  to  lie  down 
horizontally,  and  to  fold  up  into  one  plane,  as  happens  in  the  case  of 


11 


the  parallelogram  of  our  system  described  above,  the  two  points  of  ro- 
tation A and  D,  of  the  quadrilate- 
ral which  forms  the  skeleton  of  the 
service-bridge,  must  lie  on  the  cir- 
cumference of  an  ellipse,  of  which 
the  two  other  points,  B and  C,  are 
the  foci.  M.  Gouschkofsky  proposed, 
in  addition,  to  sustain  the  feet  of 
props,  not  in  a Pasqueau  hurter,  but 
in  a seat,  open  on  top,  and  fastened 
to  the  floor,  into  which  the  feet  of 
the  two  props,  joined  below  into 
one,  would  fall  automatically  when 
the  dam  was  raised.  To  lower  such 
a horse,  the  foot  of  the  prop  would 
have  to  be  lifted  out  of  the  seat  by 

a special  chain.  Without  agreeing  as  to  the  advantages  of  this  last  de- 
tail, I highly  approve  of  the  modification,  proposed  by  M.  Gouschkofsky, 
of  placing  the  point  of  rotation  of  the  bars  that  support  the  service- 
bridge  on  the  props,  instead  of  having  them  on  the  floor.  We  can  thus 
lessen  the  weight  of  metal  in  the  folding  trestles,  which  make  the 
skeleton  of  this  dam,  and  can  reduce  to  one , that  is  to  say,  to  the  mini- 
mum, the  nunber  of  points  of  fastening  and  of  rotation  on  the  floor. 

It  is  well  known  that,  in  any  system,  the  less  there  is  of  mechanism 
under  water,  the  less  danger  there  is  of  derangement ; and  on  the  other 
hand  the  greater  the  facility  of  repair  in  case  of  necessity. 

To  sum  up,  the  kind  of  movable  dam  with  horses,  which  we  have 
just  described,  and  which  is  shown  more  in  detail  on  the  annexed  draw- 
ing,  borrows  its  simplicity  from  Thenard  system,  avoids  the  construction 
of  a special  service-bridge,  which  is  necessary  with  the  Chanoine  sys- 
tem, and  whilst  preserving  the  same  advantages  as  the  Poir6e  trestle- 
system,  avoids  the  inconveniences  of  those  trestles.  We  believe  that 
this  system  is  specially  adapted  to  very  wide  rivers  with  movable  bot- 
toms, where  it  is  desirable  to  avoid  the  construction  of  intermediate 
piers. 

S.  Janicici. 

Moscow , 1882. 


B 


MOVABLE  DAM, 


Designed  by  Janicki , 

with  modifications  by  Gonschkofsky.Ing.  desPet  C.deRussie 


MOVAHLK  DAM. 

Designed  by  S.Junicki 


